Comparison of Salvage Autologous Hematopoietic Cell Transplantation with Outcomes Following Selinexor Combinations Among Double/Triple Refractory Myeloma Patients

Introduction: A vast majority of multiple myeloma (MM) patients requires subsequent lines of therapy following relapses. The choice of regimen following relapse is influenced by response, tolerance to prior therapies, as well as by disease and patient features. Treatment options are limited for those who develop triple-class refractory disease. In this setting, the role of a salvage autologous stem cell transplantation (sAHCT) is controversial. This unmet need has driven the development of new therapies with novel mechanisms of action. Selinexor, an oral selective inhibitor of nuclear export (SINE) compound, was recently approved by the FDA and EMA for use in heavily pretreated relapse refractory (RRMM) patients, including triple-class refractory RRMM and FDA has also approved the agent in patients with first relapse. In the absence of head-to-head studies, comparison of treatment options among triple-class treated patients is based on real world experience. Here we performed a retrospective comparison between outcomes following sAHCT versus Selinexor combinations administered among RRMMs.

Patients & Methods: Between January 2015 and April 2021, 22 patients at our center underwent sAHCT for treatment of refractory relapse. A transplant was defined as salvage if the patient had already received one prior AHCT and underwent a further AHCT after evidence of disease progression not responding to second generation proteasome inhibitors (PI), İmmunomodulating agents (IMID) or antiCD38 monoclonal antibody. We compared the outcomes of these patients with 10 RRMM patients who had exhausted their treatment options and were progressing on their last line of therapy to receive Selinexor, dexamethasone in combination with either bortezomib (n=7) (XVd) or carfilzomib (n=3) (XCd) as a part of a Karyopharm Expanded Access Program (KEAP). Selinexor was administered 80-100 mg po weekly in combination. Response and disease progression were assessed according to the IMWG criteria.

Results: Patients' characteristics and the outcome of treatments are shown in Table. The median age of patients was similar in both groups. Patients were heavily treated with a median of 6 prior lines of therapy (4-9) and 2 out of 10 carried high-risk cytogenetics in SVd group. Seven (31.8%) patients with high-risk cytogenetics underwent sAHCT. All patients were treated with or refractory to immunomodulators and proteasome inhibitors. Five patients responded to DCEP bridging therapy prior to sAHCT. Five patients received Selinexor after sAHCT. One patient underwent sAHCT due to progression under Selinexor treatment. In sAHCT group, 68.2% of patients relapsed within a median of 6.3 months (Figure-1). Figure-2 shows the impact of the prior lines of therapy and selinoxor on PFS.Adverse events on selinexor regimens included fatigue, nausea, thrombocytopenia which were managed with Selinexor dose adjustment and supportive care. Two patients eventually transitioned to new therapies, while 4 still remain on SVd due to continued response.

Conclusion: Our results based on a small number of patients, compared with outcomes post sAHCT reflects comparable duration of response and disease control rates with Selinexor-PI regimens among selected patients. Hospitalization and prolonged infusions are not required with the selinexor regimens, and prolonged treatment is possible with advance in lines of therapy duration of response lessens with any treatment modality. Despite of a DCEP bridging therapy prior to sAHCT, Selinexor combos have achieved similar PFS even among triple class refractory MM patients. For countries where CAR-T therapies are not accessible, sAHCT and Selinexor combinations may be considered as a valid clinical option after failing CD38 monoclonal antibodies, PI and IMIDs. These data support the use of selinexor-based regimens in the treatment of relapsed MM, and given the potency of the combinations, in earlier lines of therapy including in patients who have received anti-CD38 mAbs.

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